SuperKEKB

SuperKEKB. It is a major asymmetric-energy electron–positron collider located at the High Energy Accelerator Research Organization (KEK) in Tsukuba, Japan. As a major upgrade to the highly successful KEKB collider, its primary purpose is to host the Belle II experiment in the search for new physics beyond the Standard Model. The facility aims to achieve a world-record instantaneous luminosity, enabling the collection of unprecedented data samples from the decays of B mesons, charm hadrons, and tau leptons.

Overview

SuperKEKB represents the forefront of high-energy physics research in Japan, operating as a particle accelerator complex dedicated to precision measurements. The collider is designed to produce copious amounts of B meson pairs and other particles through collisions at the energy of the Upsilon(4S) resonance. This strategy follows the legacy of the earlier Belle experiment and the BaBar experiment at the Stanford Linear Accelerator Center, which first observed CP violation in the B meson system. The international Belle II collaboration, involving hundreds of scientists from dozens of countries, is responsible for the detector and data analysis. The project's ultimate goal is to uncover subtle discrepancies from Standard Model predictions that could point to phenomena like dark matter or new sources of CP violation.

Design and Components

The accelerator complex reuses the existing 3-kilometer tunnel from KEKB but implements a novel "nano-beam" collision scheme, a concept pioneered by the INFN-led team for the SuperB project. Key components include a new positron source, upgraded radio frequency systems, and extensively modified storage rings. The electron ring operates at 7 GeV, while the lower-energy 4 GeV positron ring uses a unique "large Piwinski angle" design to squeeze beams to nanometer-scale vertical sizes at the interaction point. This is achieved with advanced superconducting final focusing quadrupole magnets and sophisticated beam optics. Critical particle injection is handled by the LINAC facility, which also supplies beams to other facilities like the Japan Proton Accelerator Research Complex.

Physics Goals and Experiments

The core scientific program is conducted by the Belle II experiment, which features a completely upgraded detector surrounding the interaction point. Physics goals are extensive, focusing on ultra-precise measurements of CP violation, lepton flavor violation, and rare decays of B mesons and D mesons. Researchers will intensively study quark mixing parameters within the Cabibbo–Kobayashi–Maskawa matrix and search for signs of lepton universality violation, an area where previous experiments like LHCb at CERN have reported intriguing anomalies. Additional programs include detailed spectroscopy of charmonium states, studies of tau lepton properties, and direct searches for exotic particles such as dark photons and long-lived particles predicted by theories like supersymmetry.

Performance and Achievements

After a commissioning phase, SuperKEKB began its physics run, steadily increasing its peak luminosity and challenging the records set by its predecessor and other colliders like the Beijing Electron–Positron Collider. It has already demonstrated the feasibility of its innovative nano-beam scheme in a real collider environment. The Belle II experiment has collected a substantial integrated luminosity, allowing for early physics results on topics like B meson lifetimes and searches for rare decays. These achievements validate the complex accelerator physics and detector performance, establishing the facility as a unique and complementary probe to the high-energy frontier explored by the Large Hadron Collider.

Timeline and History

The project was formally proposed following the conclusion of the highly successful KEKB and Belle experiment in 2010, which had confirmed the Kobayashi-Maskawa theory. Major construction and upgrade work began around 2010, involving a global collaboration. The first beam tests for the new rings occurred in 2016, followed by the commissioning of the full collider and the installation of the Belle II detector. The official start of physics data-taking was announced in 2018. The project builds upon decades of expertise from the original TRISTAN project at KEK and benefits from international technological contributions from institutions like the Budker Institute of Nuclear Physics and the University of Hawaii.

Category:Particle accelerators Category:Research facilities in Japan Category:High Energy Accelerator Research Organization